The invention relates to the field of bulk thermal radiation emitters, and in particular to a vertical-cavity enhanced resonant thermal emitter (VERTE).
Bulk thermal emission sources are commonly perceived as isotropic, broad-band and incoherent electromagnetic radiation sources. Although different bulk materials exhibit different emission characteristics, tailoring emission properties require engineering new material systems and structures that interact with sources of radiation (fluctuating thermal sources) on a wavelength scale. Indeed, structures with feature sizes on the order of radiation wavelengths (such as photonic crystals (PhC)) exhibit qualitatively different radiation behavior due to intricate interaction between the radiation and the matter. The ability to modulate photonic density of states and hence modify spontaneous emission rates in photonic crystals opens immense possibilities for designing novel thermal sources.
A majority of the previous work on thermal radiation properties of 1D, 2D and 3D photonic crystals investigates the suppression and enhancement of thermal emission for wide range of wavelengths. However, in this work the invention is particularly interested in narrow-band, antenna-like thermal emission from PhC structures. Previously, it was shown that surface patterned materials (with surface grating or 2D photonic crystal) that support surface polaritons (plasmon-polariton or phonon-polariton) can have narrow angular and narrow-band thermal radiation properties resulting in increased spatial and temporal coherence in the far-field and. Thermal emission properties of these structures allow certain degrees of freedom in adjusting the emission peak wavelength and directionality. Antenna-like emission patterns were also noticed with even simple planar structures like thin-film emitters. In 3D tungsten PhC, strong resonant enhancement near the band-edge was observed which can also suggest increased spatial coherence. Yet this structure shows a large emissivity outside the photonic bandgap which makes it unsuitable for applications that require highly selective emission properties.